Plasmodium lophurae contained a serine hydroxymethyltransferase (EC 2.1.2.1) which was partially purified and characterized by ammonium sulfate fractionation and chromatography on Sephadex G-100. The enzyme was precipitated by 3.0 to 3.3 M ammonium sulfate and had a molecular weight of 68,300 by exclusion chromatography on G-100. The pH optimum of the enzyme was broad, 6.8 to 7.6, in sodium phosphate-citrate buffer. Citrate stabilized the enzyme during storage in phosphate buffer at 4 degrees C. The Km for L-serine was 4.3 x 10 to the 3rd power M and 2.5 x 10 to the 4th power M for tetrahydrofolate. BIBLIOGRAPHIC REFERENCE: Platzer, E.G. and H.C. Campuzano. 1976. The serine hydroxymethyltransferase of Plasmodium lophurae. Submitted to J. Protozoology.